Building Secure and Efficient Docker Images: Best Practices

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DOs:

1. Use Official Images

Always rely on validated Docker images from official repositories.

docker pull ubuntu:20.04

2. Specify Base Image Version

Avoid using `latest` tag to prevent unexpected updates.

FROM python:3.9-slim

3. Secure Image Builds with Multi-Stage

Reduce attack surface by discarding build dependencies.

FROM golang:1.18 AS builder 
WORKDIR /app 
COPY . . 
RUN go build -o myapp

FROM alpine:latest 
COPY --from=builder /app/myapp /usr/local/bin/ 
CMD ["myapp"]

4. Prefer `COPY` Over `ADD`

`COPY` is more transparent and predictable.

COPY ./src /app/src

5. Parameterize Builds with `ARG`

Use build-time variables for flexibility.

ARG APP_VERSION=1.0 
ENV APP_VERSION=${APP_VERSION}

6. Set `WORKDIR` Early

Define working directory before `COPY`/`RUN`.

WORKDIR /app 
COPY . .

DON’Ts:

1. Ignore Image Efficiency

Avoid unnecessary layers—combine `RUN` commands.

RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/

2. Overload Build Context

Use `.dockerignore` to exclude unwanted files.

.log 
.git

3. Hardcode Credentials

Use Docker secrets or environment variables.

docker run -e DB_PASSWORD=secret myimage

4. Run as Root

Always use a non-root user.

RUN useradd -m appuser && chown -R appuser /app 
USER appuser

5. Create Multipurpose Containers

Follow the “one process per container” rule.

6. Omit `ENTRYPOINT`

Define `ENTRYPOINT` for consistent execution.

ENTRYPOINT ["python"] 
CMD ["app.py"]

You Should Know:

Security Hardening Commands

  • Scan images for vulnerabilities:
    docker scan ubuntu:20.04
  • Remove unused images:
    docker image prune -a
  • Inspect image layers:
    docker history myimage

Linux Commands for Docker Debugging

  • Check container processes:
    docker top <container_id>
  • Analyze container logs:
    docker logs --tail 100 <container_id>
  • Inspect network configuration:
    docker inspect --format='{{.NetworkSettings.IPAddress}}' <container_id>

Windows Docker Commands

  • Clean unused data:
    docker system prune --volumes
  • Run Windows container:
    docker run -it mcr.microsoft.com/windows/servercore:ltsc2022 cmd

What Undercode Say:

Adopting these practices ensures lightweight, secure, and maintainable Docker images. Multi-stage builds and non-root users mitigate risks, while `.dockerignore` and layer optimization boost performance.

Expected Output:

A production-ready Docker image with:

  • Minimal attack surface
  • Version-pinned dependencies
  • Non-root execution
  • Efficient layer caching

Prediction:

Container security will increasingly integrate with Kubernetes-native tooling (e.g., Falco, Kyverno) for runtime enforcement.

URLs (if needed):

IT/Security Reporter URL:

Reported By: Parasmayur Learning – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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